In the prior art, methylation of aniline with methanol was conducted in a batch reactor. Either sulfuric acid or phosphoric acid was used as the catalyst in the liquid-phase reaction that took place at a temperature of about 200.degree. C. under a pressure of from 30 to 50 kg/cm.sup.2. This traditional route suffers from the disadvantages of high capital cost, the corrosion of the reactor, and the need for waste acid treatment. The more recent vapor-phase technology has overcome corrosion problems and waste acid treatment but did not solve all the shortcomings associated with the liquid-phase reaction.
U.S. Pat. No. 3,558,706 discloses a process for the preparation of N-methylaniline by the reaction of 1 mole of aniline with 6 moles of methanol at 500.degree..+-.50.degree. C. at 1 atmosphere over a catalyst consisting of 4MgCO.sub.3.Mg(OH).sub.2.4H.sub.2 O. The liquid hourly space velocity (LHSV) based on aniline was 0.3 to 1.0 hr.sup.-1, and the optimum yield was 68%. The reaction required high temperatures, wasted methanol, and produced unimpressive results.
Japan Kokkai 74/81331 describes a process for making N,N-dimethylaniline by the liquid-phase reaction of aniline with methanol in the presence of a solid acid Al.sub.2 O.sub.3 -SiO.sub.2, Y-type zeolite catalyst at 280.degree. C. to give 98.1% N,N-dimethylaniline. In order to obtain the end product, a three hour reaction time and a reaction pressure of 150 kg/cm.sup.2 was required. In addition to the disadvantages previously mentioned, these processes have limited flexibility as far as the control of the N-alkyl to N,N-dialkylaniline ratio was concerned, and therefore could not meet market demand.
The use of transition metal zeolites has also been described for the vapor phase catalytic N-methylation of aniline with methanol over a temperature range of 200.degree. to 300.degree. C. (Takamiya et al., "N-Methylation of Aniline with Methanol over Transition Metal Zeolite", Weseda University Report 21 (1975)). In this work, the catalysts were obtained by ion-exchanging HY zeolites with transition metal nitrate solution. The ion-exchanged Y zeolites, however, proved to be less active than the parent HY catalyst and gave poor control with regard to product selection.